Lens barrel

ABSTRACT

A lens barrel includes a front lens frame supporting a front lens group; a rear lens frame supporting a rear lens group; a cam ring including first and second cam grooves which receive first and second cam followers of the front and rear lens frames; the first and second cam grooves include first and second moving sections and first and second accommodation sections, respectively; and a guiding mechanism allowing the rear lens frame to relatively rotate when the second cam follower engages in a vicinity an accommodation position of the second accommodation section, and prohibiting the rear lens frame from relatively rotating while allowing the rear lens frame to only relatively move in the optical axis direction when the second cam follower engages in a section of the second cam groove which includes the second moving section and excludes this vicinity.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a lens barrel which can be used as aphotographing lens barrel of a camera.

2. Description of the Related Art

A conventional lens barrel in which each of linearly guided front andrear lens groups is provided with a set of follower pins which arerespectively engaged in a corresponding set of cam grooves (cam slots)formed on a rotating cam ring so that the linearly guided front and rearlens groups move in an optical axis direction without rotating about theoptical axis by rotation of the cam ring to move each of the front andrear lens groups between an accommodation position and aready-to-photograph position in front of the accommodation is known inthe art.

However, if the diameter of the cam ring is small, a reduction of thepitch of each cam groove (i.e., a reduction of the angle of inclinationof each cam groove relative to a circumferential direction of the camring) causes the set of cam grooves for the first lens group and the setof cam grooves for the second lens group to interfere with each other,or causes the front and rear lens groups positioned at their respectiveaccommodation positions to interfere with each other, to thereby getstuck (jam) thereat even if the cam ring is rotated to move the firstand second lens groups forward from their respective accommodationpositions.

Among such type of lens barrels, in a lens barrel required to bedesigned compact as much as possible, it is sometimes desirable not torotate the cam ring for the purpose of preventing the cam ring frominterfering with any peripheral elements while moving the cam ring inthe optical axis direction in a predetermined moving section of the camring from a fully retracted position thereof.

Moreover, in the above described conventional type of lens barrels,backlash occurs between the cam ring and a guiding mechanism for guidingthe cam ring in the optical axis direction when the cam ring is moved toa ready-to-photograph position thereof. Such backlash deteriorates theperformance of the focusing system.

SUMMARY OF THE INVENTION

The present invention provides a lens barrel having front and rear lensgroups and a cam ring on which cam grooves for driving the front andrear lens groups are formed, wherein front and rear lens groups can bedriven to move forward smoothly from their respective accommodationpositions in an optical axis direction by rotation of the cam ring evenif the angle of inclination of each cam groove formed thereon withrespect to a circumferential direction of the cam ring is small.

The present invention provides a lens barrel in which the cam ring isprevented from interfering with any peripheral elements while moving inthe optical axis direction in a predetermined moving section of the camring from a fully retracted position thereof.

The present invention provides a lens barrel in which backlash isprevented from occurring between the cam ring and a guiding mechanismfor guiding the cam ring in the optical axis direction with a simplemechanism.

For example, in an embodiment, a lens barrel is provided, including afront lens frame which supports a front lens group and includes a firstcam follower, the front lens frame being guided linearly in an opticalaxis direction without rotating about the optical axis; a rear lensframe which supports a rear lens group and includes a second camfollower; a cam ring driven to rotate about the optical axis, the camring including a first cam groove and a second cam groove in which thefirst cam follower and the second cam follower are respectively engaged;the first cam groove including a first moving section for moving thefront lens frame in the optical axis direction, and a firstaccommodation section for moving the front lens frame behind a positionof the front lens frame of which the first follower is engaged in thefirst moving section; the second cam groove including a second movingsection for moving the rear lens frame in the optical axis direction,and a second accommodation section for moving the rear lens frame behinda position of the rear lens frame of which the second follower isengaged in the second moving section, the second accommodation sectionincluding an accommodation position at which the rear lens frame ispositioned rearmost; and a guiding mechanism, provided between the frontlens frame and the rear lens frame, for allowing the rear lens frame torotate about the optical axis relative to the front lens frame when thesecond cam follower is engaged in a vicinity of the accommodationposition of the second accommodation section, and for prohibiting therear lens frame from rotating about the optical axis relative to thefront lens frame while allowing the rear lens frame to move only in theoptical axis direction relative to the front lens frame when the secondcam follower is engaged in a section of the second cam groove whichincludes the second moving section and excludes the vicinity of theaccommodation position.

The lens barrel can further include a shutter unit fixed to the rearlens frame; and a flexible PWB which extends rearward from the shutterunit so that a drive signal can be transmitted to the shutter unit viathe flexible PWB.

The lens barrel can further include an elastic band which is engagedwith the flexible PWB to pull a portion of the flexible PWB in adirection away from the optical axis.

The elastic band can be a rubber band.

The multi-direction guiding mechanism can include a linear guide grooveformed on an inner peripheral surface of the front lens frame to extendparallel to the optical axis; a rotation-permitting groove, formed at afront end of the linear guide groove, which communicatively connectswith the linear guide groove, a width of the rotation-permitting groovebeing greater than a width of the linear guide groove in acircumferential direction of the front lens frame; and a linear guideprojection, formed on the rear lens frame, which is engaged in therotation-permitting groove when the second cam follower is engaged inthe vicinity of the accommodation position, and which is engaged in thelinear guide groove when the second cam follower is engaged in thesection of the second cam groove which includes the second movingsection and excludes the vicinity of the accommodation position.

The front lens frame can include an inner flange for supporting thefront lens group, a circumferential opening being formed on the frontlens frame. The rear lens frame can include a front projecting portion,on which the linear guide projection is formed, the front projectingportion projecting forward to extend through the inner flange throughthe circumferential opening when the second cam follower is engaged inthe vicinity of the accommodation position.

The inner flange can be formed on the front lens frame at a front endthereof.

The lens barrel can be a zoom lens barrel, wherein the first movingsection and the second moving section constitute a first zooming sectionand a second zooming section for moving the front lens group and therear lens group to perform a zooming operation, respectively.

The rear lens frame can rotate about the optical axis via rotation ofthe cam ring when the second cam follower is engaged in the vicinity ofthe accommodation position.

In another embodiment, a lens barrel is provided, including a front lensframe which supports a front lens group and includes a first camfollower, the front lens frame being guided linearly in an optical axisdirection without rotating about the optical axis; a rear lens framewhich supports a rear lens group and includes a second cam follower; acam ring driven to rotate about the optical axis, the cam ring includinga continuous cam groove in which the first cam follower and the secondcam follower are engaged; wherein the continuous cam groove includes afirst moving section for moving the front lens group in the optical axisdirection; a first accommodation section for moving the front lens framebehind a position of the front lens frame of which the first follower isengaged in the first moving section; a second moving section for movingthe rear lens group in the optical axis direction; and a secondaccommodation section for moving the rear lens frame behind a positionof the rear lens frame of which the second follower is engaged in thesecond moving section, the second accommodation position including anaccommodation position at which the rear lens frame is positionedrearmost, in that order from one end of the continuous cam groove; and aguiding mechanism for allowing the rear lens frame to rotate about theoptical axis relative to the front lens frame when the second camfollower is engaged in a vicinity of the accommodation position of thesecond accommodation section, and for prohibiting the rear lens framefrom rotating about the optical axis relative to the front lens framewhile allowing the rear lens frame to move only in the optical axisdirection relative to the front lens frame when the second cam followeris engaged in a section of the second cam groove which includes thesecond moving section and excludes the vicinity of the accommodationposition. The second accommodation section is formed to firstly make therear lens frame move in the optical axis direction while making the rearlens frame rotate about the optical axis relative to the front lensframe via the second cam follower engaged in the second accommodationsection, and to subsequently make the front lens frame guide the rearlens frame in the optical axis direction without making the rear lensframe rotate about the optical axis when the first cam follower of thefront lens frame moves from the first accommodation section to thesecond moving section by rotation of the cam ring.

The lens barrel can be a zoom lens barrel, wherein the first movingsection and the second moving section constitute a first zooming sectionand a second zooming section for moving the front lens group and therear lens group to perform a zooming operation, respectively.

The guiding mechanism can include a guiding portion formed on the frontlens frame, wherein the front lens frame firstly comes into contact withthe rear lens frame and subsequently presses the rear lens frame to movethe rear lens frame forward in the optical axis direction when the firstcam follower passes the second moving section while moving from thefirst accommodation section toward the first moving section; and anengaging portion formed on the rear lens frame, the engaging portionbeing engaged with the guiding portion to be guided linearly in theoptical axis direction by the guiding portion, wherein a side edge ofthe second accommodation section firstly comes into contact with thesecond cam follower, and subsequently the side edge presses the secondcam follower to rotate the rear lens frame about the optical axis sothat the engaging portion enters the guiding portion when the rear lensframe is moved forward by the front lens frame.

In another embodiment, a lens barrel is provided, having an opticalsystem having a plurality of lens groups, the lens barrel including alens supporting frame to which a frontmost lens group of the pluralityof lens groups is fixed; a first moving frame to which the lenssupporting frame is screw-engaged; a second moving frame to which a rearlens group of the plurality of lens groups which is positioned behindthe frontmost lens group is supported; and a support frame movementmechanism for moving the first moving frame and the second moving framebetween respective ready-to-photograph positions and respectiveaccommodation positions located behind the respectiveready-to-photograph positions in an optical axis direction. The supportframe movement mechanism makes the first moving frame and the secondmoving frame rotate about the optical axis relative to each other withthe lens supporting frame and the second moving frame being in contactwith each other when the first moving frame and the second moving frameare respectively positioned in the vicinity of the respectiveaccommodation positions. One of the lens supporting frame and the secondmoving frame includes a low-frictional portion provided on a contactingsurface thereof.

The low-frictional portion can be a low-frictional sheet fixed to thecontacting surface.

A fixing position of the lens supporting frame relative to the firstmoving frame in the optical axis direction can be adjusted via thescrew-engagement therebetween during assembly.

The low-frictional sheet can be fixed to a contacting surface of thesecond moving frame which comes into sliding contact with a contactingsurface of the lens supporting frame.

The lens barrel can be a zoom lens barrel.

In another embodiment, a lens barrel is provided, having at least onemovable lens frame and a cam ring for moving the movable lens frame in adirection of an optical axis via a movement of the cam ring which isrotatable about the optical axis and movable in the optical axisdirection, the lens barrel including a stationary ring provided around,and coaxial with, the cam ring; a rotatable ring provided around, andcoaxial with, the stationary barrel, the rotatable ring being driven torotate about the optical axis; a cam follower which extends radiallyoutwards from the cam ring; and a cam through-slot and a rotationtransfer groove which are formed on the stationary ring and therotatable ring, respectively, so that the cam follower is engaged in thecam through-slot and corresponding the rotation transfer groove. The camthrough-slot includes a linear slot portion which extends parallel tothe optical axis; and an inclined slot portion which extends in adirection inclined to both the optical axis direction and acircumferential direction of the stationary ring. The rotation transfergroove includes an inclined groove portion in which the cam follower isengaged when the cam follower is engaged in the linear slot portion, anda linear groove portion in which the cam follower is engaged when thecam follower is engaged in the inclined slot portion.

The linear slot portion can be formed on the stationary barrel at aposition to fully retract the cam ring.

The movable lens frame can include a front movable lens frame and a rearmovable lens frame; the lens barrel further including a linear guidering which guides the front movable lens frame linearly in the opticalaxis direction without rotating the front movable lens frame about theoptical axis; and a biasing device provided between the linear guidering and the front movable lens frame, for biasing the front movablelens frame rearwards. Each of the front movable lens frame and the rearmovable lens frame moves to an accommodation position thereof via abiasing force of the biasing device when the cam follower of the camring moves along the linear slot portion toward an end thereofcorresponding to an accommodation position of the cam ring.

The lens barrel can be a zoom lens barrel.

The biasing device can include at least one helical compression spring.

In another embodiment, a lens barrel is provided, in which a movablelens frame is driven in an optical axis direction via rotation of a camring, the lens barrel including a cam follower which extends radiallyoutwards from the cam ring; a stationary barrel provided around, andcoaxial with, the cam ring, the stationary barrel including a camthrough-slot in which the cam follower is engaged, the cam through-slotincluding a lens-frame-driving slot portion for moving the movable lensframe in the optical axis direction in a predetermined operating range;and a biasing ring for biasing the cam ring toward the stationary ringin the optical axis direction. The biasing ring includes a contactingsurface which comes into contact with a portion of the cam followerwhich projects radially outwards from the cam through-slot to press theportion of the cam follower against a side edge of the cam through-slotwhen the cam follower is engaged in the lens-frame-driving slot portionof the cam through-slot.

The biasing ring can include a projection, a rear end surface thereofconstituting the contacting surface.

It is desirable for the cam through-slot to extends in a circumferentialdirection of the stationary barrel.

The lens barrel can further include a rotatable ring provided around,and coaxial with, the stationary barrel, the rotatable ring being drivento rotate about the optical axis. The rotatable ring includes a rotationtransfer groove formed on an inner peripheral surface of the rotatablering so that the cam follower is engaged in the cam through-slot and acorresponding the rotation transfer groove, the cam ring being rotatedby rotation of the rotatable ring via engagement of the cam followerwith the rotation transfer groove.

The lens barrel can further include a biasing device which biases thebiasing ring and the rotatable ring to approach each other in theoptical axis direction; wherein the biasing ring is mounted to therotatable ring via the biasing device.

The lens barrel can further include a rotatable ring provided around,and coaxial with, the stationary barrel and driven to rotate about theoptical axis, the rotatable ring including a rotation transfer grooveformed on an inner peripheral surface of the rotatable ring so that thecam follower is engaged in the cam through-slot and a corresponding therotation transfer groove, the cam ring being rotated by rotation of therotatable ring via engagement of the cam follower with the rotationtransfer groove; and a biasing device which biases the biasing ring andthe rotatable ring to approach each other in the optical axis direction.The biasing ring is mounted to the rotatable ring via the biasingdevice. The projection is formed on the biasing ring to extend radiallyinwards to extend through the rotatable ring through a through holeformed on the rotatable ring immediately in front of the rotationtransfer groove.

The lens barrel can be a zoom lens barrel, the lens-frame-driving slotportion constituting a zooming slot portion for moving the movable lensframe in the optical axis to perform a zooming operation.

The present disclosure relates to subject matter contained in JapanesePatent Applications Nos. 2001-83685, 2001-83686, 2001-83687, 2001-83688and 2001-83689 (all filed on Mar. 22, 2001) which are expresslyincorporated herein by reference in their entireties.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be described below in detail with referenceto the accompanying drawings in which:

FIG. 1 is an exploded perspective view of an embodiment of a zoom lensbarrel according to the present invention;

FIG. 2 is an exploded perspective view of an upper left portion of thezoom lens barrel shown in FIG. 1;

FIG. 3 is an exploded perspective view of a middle portion of the zoomlens barrel shown in FIG. 1;

FIG. 4 is an exploded perspective view of a lower right portion of thezoom lens barrel in FIG. 1;

FIG. 5 is an axial cross sectional view of the zoom lens barrel shown inFIG. 1, above the optical axis, showing the zoom lens barrel in anaccommodation state;

FIG. 6 is an axial cross sectional view of the zoom lens barrel shown inFIG. 1, above the optical axis, taken along a plane different from thatof FIG. 5, showing the zoom lens barrel in an accommodation state;

FIG. 7 is an axial cross sectional view of the zoom lens barrel shown inFIG. 1, showing the zoom lens barrel in an accommodation state above theoptical axis, and further showing the zoom lens barrel in aready-to-photograph state below the optical axis;

FIG. 8 is a developed view of an outer peripheral surface of a cam ringprovided as an element of the zoom lens barrel shown in FIG. 1;

FIG. 9 is a developed view of one of three cam grooves formed on aninner peripheral surface of the cam ring, showing the profile of the camgroove;

FIG. 10 is a developed view of two of the three cam grooves shown inFIGS. 8 and 9, showing the relationship between the cam grooves, firstfollower pins formed on a first lens frame, and second follower pinsformed on a second lens frame;

FIG. 11 is a schematic developed view of a cam-ring-control cam slotformed on a stationary ring and an associated rotation transfer grooveformed on a rotatable ring;

FIG. 12 is a front elevational view of the zoom lens barrel with abarrier blade support front plate removed therefrom in a state where apair of lens barrier blades are closed;

FIG. 13 is a view similar to that of FIG. 12 and illustrates the barrierdrive ring and peripheral elements thereof in a state where the pair oflens barrier blades are open;

FIG. 14 is a view similar to that of FIG. 12 and illustrates the pair ofbarrier blades of a barrier unit, showing the relationship between thepair of barrier blades and an inner ring;

FIG. 15 is a graph showing variations of respective axial positions offirst and second lens groups (first and second lens frames) in a rangeof movement including a zooming section and a retracting section;

FIG. 16 is a developed view of the cam ring and the barrier drive ring,showing the positional relationship therebetween; and

FIG. 17 is an enlarged perspective view of a lens barrier blade shown inFIGS. 1 and 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 is an exploded perspective view of an embodiment of an extendablezoom lens barrel for a digital camera. The zoom lens barrel 1 isprovided with a guiding mechanism (support frame movement mechanism)which includes a set of three linear guide grooves (guiding portions) 18c of a first lens group moving frame (front lens frame) 18, a set ofthree circumferential recesses (rotation-permitting grooves) 18 h of thefirst lens group moving frame 18, and a set of three linear guide keys(linear guide projections/engaging portions) 19 a of the second lensgroup moving frame (rear lens frame) 19. The zoom lens barrel 1 isfurther provided with a support-frame drive mechanism which includes aset of three follower pins 18 f of the first lens group moving frame 18,a set of three follower pins 19 f of the second lens group moving frame19, a cam ring 15, a set of three linear guide holes 18 a of the firstlens group moving frame 18, a set of three linear guide bosses 17 d ofan inner ring 17, the set of three linear guide grooves 18 c of thefirst lens group moving frame 18, and a set of three linear guide keys19 a of the second lens group moving frame 19.

As can be clearly seen in FIGS. 5 through 7, the zoom lens barrel 1 isprovided with a photographing optical system including three lensgroups: a first lens group L1, a second lens group L2 and a third lensgroup L3, in that order from the object side (the left side as viewed ineach of FIGS. 5 through 7) The first and second lens groups L1 and L2are driven to move along an optical axis O relative to the third lensgroup L3 while varying the distance therebetween to perform zoomingoperation. The third lens group L3 serves as a focusing lens group, andis driven to move along the optical axis O to perform focusingoperation.

The zoom lens barrel 1 is provided with a housing 11, a shaft holdingmember 12 and a stationary ring 13, which are all stationary membersfixed to a camera body (not shown). Accordingly, the housing 11, theshaft holding member 12 and the stationary ring 13 do not move in thedirection of the optical axis O (i.e., in the optical axis direction) orrotates about the optical axis O. The housing 11 is provided at a rearend thereof with a flange 11 a (see FIG. 4), while the stationary ring13 is provided at a rear end thereof with a flange 13 a which is fixedto the flange 11 a of the housing 11. The housing 11 is provided with anouter cylindrical portion 11 b and a filter holding portion 11 c towhich a low-pass filter 11 d is fixed. As shown in FIGS. 5 through 7,the low-pass filter 11 d is positioned in front of a CCD (solid-stateimage pick-up device) 10 a fixed to a stationary base 10 positioned inthe camera body.

The stationary ring 13 is positioned inside the outer cylindricalportion 11 b of the housing 11. The zoom lens barrel 1 is provided, onthe stationary ring 13 between the stationary ring 13 and the outercylindrical portion 11 b, with a rotatable ring 14. The stationary ring13 is positioned inside the rotatable ring 14 which supports the camring 15 therein. The stationary ring 13 is provided with a set of threecam slots (cam through-slots) 13 b formed on the stationary ring 13 asthrough-slots at equi-angular intervals in a circumferential directionthereof. The cam ring 15 is provided at the rear end thereof with athick-wall cylinder portion 15 a. A set of three follower pins (camfollowers) 15 b fixed to the thick-wall cylinder portion 15 a atequi-angular intervals in a circumferential direction of the cam ring 15pass through the set of three cam slots 13 b of the stationary ring 13to be engaged in a set of three rotation transfer grooves 14 a (only ofwhich appears in FIGS. 1 and 4) which are formed on an inner peripheralsurface of the rotatable ring 14.

FIG. 11 shows a developed view of one of the three cam slots 13 b andthe associated one of the three rotation transfer grooves 14 a. Eachrotation transfer groove 14 a includes a linear groove portion 14 a 1,an inclined groove portion 14 a 2, and a circumferential groove portion14 a 3 in that order from the front end to the rear end of the lineargroove portion 14 a 1 (from left to right as viewed in FIG. 11). Thelinear groove portion 14 a 1, which occupies a major portion of therotation transfer groove 14 a, extends parallel to the optical axis O.The circumferential groove portion 14 a 3 of each rotation transfergroove 14 a is used only when the zoom lens barrel 1 isassembled/disassembled. Each cam slot 13 b includes a linear slotportion 13 b 1, a state-changing slot portion (inclined slot portion) 13b 2, a zooming slot portion (lens-frame-driving slot portion) 13 b 3,and a terminal slot portion 13 b 4, in that order from the end (thelower end as viewed in FIG. 11) of the cam slot 13 b which closest tothe rear end of the stationary ring 13. The linear slot portion 13 b 1extends parallel to the optical axis O. The state-changing slot portion13 b 2 extends in a direction inclined with respect to both the opticalaxis O and a circumferential direction of the stationary ring 13. Thezooming slot portion 13 b 3 extends in a circumferential direction ofthe stationary ring 13. The terminal slot portion 13 b 4 is used onlywhen the zoom lens barrel 1 is assembled/disassembled.

The rotating barrel 14 rotates about the optical axis O in a rotationalrange between an accommodation position (accommodation position) and atelephoto extremity via a wide-angle extremity. This rotational rangeincludes a preparation section (preparation stage) which extends betweenthe accommodation position and the wide-angle extremity, and a zoomingsection which extends between the wide-angle extremity to the telephotoextremity (see FIG. 11). If the rotatable ring 14 rotates relative tothe stationary ring 13 in a state where each follower pin 15 b isengaged in the inclined groove portion 14 a 2 of the associated rotationtransfer groove 14 a and the linear slot portion 13 b 1 of theassociated cam slot 13 b (i.e., in a state where the rotatable ring 14is in the accommodation position and where the cam ring 15 is fullyretracted), each follower pin 15 b of the cam ring 15 is pressed by aside edge of the linear slot portion 13 b 1 of the associated cam slot13 b, which causes the cam ring 15 to move in the optical axis directionalong the linear slot portion 13 b 1 without rotating about the opticalaxis O. If the rotatable ring 14 rotates relative to the stationary ring13 in a state where each follower pin 15 b is engaged in the lineargroove portion 14 a 1 of the associated rotation transfer groove 14 aand the state-changing slot portion 13 b 2 of the associated cam slot 13b (i.e., in a state where the rotatable ring 14 is in the preparationsection), each follower pin 15 b of the cam ring 15 moves along thestate-changing slot portion 13 b 2 of the associated cam slot 13 b,which causes the cam ring 15 to rotate about the optical axis O whilemoving in the optical axis direction due to the engagement of thefollower pin 15 b with the state-changing slot portion 13 b 2. If therotatable ring 14 rotates relative to the stationary ring 13 in a statewhere each follower pin 15 b is engaged in the linear groove portion 14a 1 of the associated rotation transfer groove 14 a and the zooming slotportion 13 b 3 of the associated cam slot 13 b (i.e., in a state wherethe A-rotatable ring 14 is in the zooming section), each follower pin 15b of the cam ring 15 moves along the zooming slot portion 13 b 3 of theassociated cam slot 13 b, which causes the cam ring 15 to rotate aboutthe optical axis O without moving in the optical axis direction.

The rotatable ring 14 is provided on an outer peripheral surface thereofwith a circumferential gear 14 b which is in mesh with a drive pinion(not shown). The drive pinion is driven by a reversible motor (notshown) to rotate forwardly and reversely. Rotation of the drive pinioncauses the rotatable ring 14 to rotate to thereby move the cam ring 15in the optical axis direction while rotating about the optical axis O.Accordingly, if the accomodation position of the cam ring 15 is regardedas a starting position (reference position) of movement of the cam ring15, firstly the cam ring 15 moves linearly in the optical axis directionwithout rotating about the optical axis O (due to the linear slotportions 13 b 1), subsequently the cam ring 15 moves in the optical axisdirection while rotating about the optical axis O (due to thestate-changing slot portions 13 b 2 in the preparation section), andfinally the cam ring 15 rotates about the optical axis O without movingin the optical axis direction (due to the zooming slot portion 13 b 3 inthe zooming section).

In the present embodiment of the zoom lens barrel 1, the rotatable ring14, the cam ring 15 and a barrier drive ring 31 are rotatable elements.The remaining movable elements, except for the second lens group movingframe 19, linearly move in the optical axis direction without rotatingabout the optical axis O. The second lens group moving frame 19 canrotate about the optical axis O slightly. Such linearly moving elementsand guiding mechanisms thereof will be hereinafter discussed. The zoomlens barrel 1 is provided between the stationary ring 13 and the camring 15 with an outer ring 16 and the inner ring 17 which is providedinside the outer ring 16. The outer ring 16 and the inner ring 17 arepositioned in an annular space between the cam ring 15 and thestationary ring 13, while the thick-wall cylinder portion 15 a of thecam ring 15 is engaged with an inner peripheral surface of thestationary ring 13 so that the cam ring 15 can rotate about the opticalaxis O relative to the stationary ring 13 without tilting relative tothe optical axis O.

As shown in FIG. 2, the outer ring 16, which is positioned immediatelyinside of the stationary ring 13, includes a main ring body 16 r and areinforcing ring 16 x which are made of synthetic resin and metal,respectively. The main ring body 16 r is provided at a rear end thereofwith a thick-wall cylinder portion 16 a, and is further provided, on thethick-wall cylinder portion 16 a at equi-angular intervals in acircumferential direction of the main ring body 16 r, with a set ofthree linear guide keys 16 b (only one of which appears in FIGS. 1 and2) which extend radially outwards. The stationary ring 13 is provided onan inner peripheral surface thereof with a set of three linear guidegrooves 13 c which extend parallel to the optical axis O, and in whichthe set of three linear guide keys 16 b of the main ring body 16 r areslidably engaged in the set of three linear guide grooves 13 c,respectively. The metal reinforcing ring 16 x is fitted on, and adheredto, an outer peripheral surface of the main ring body 16 r in front ofthe thick-wall cylinder portion 16 a by an adhesive to reinforce themain ring body 16 r with a minimum increase in wall thickness of theouter ring 16, which contributes to a reduction in wall thickness of thezoom lens barrel 1, i.e., contributes to further miniaturization of thezoom lens barrel 1.

Similar to the outer ring 16, the inner ring frame 17 includes a mainring body 17 r and a reinforcing ring 17 x which are made of syntheticresin and metal, respectively. The main ring body 17 r is provided at arear end thereof with a thick-wall cylinder portion 17 a. The metalreinforcing ring 17 x is fitted on and adhered to an outer peripheralsurface of the main ring body 17 r in front of the thick-wall cylinderportion 17 a by an adhesive to reinforce the main ring body 17 r with aminimum increase in wall thickness of the inner ring 17, whichcontributes to a reduction in wall thickness of the zoom lens barrel 1,i.e., contributes to further miniaturization of the zoom lens barrel 1.

The outer ring 16 is provided, on an inner peripheral surface of themain ring body 16 r at equi-angular intervals in a circumferentialdirection of the outer ring 16, with a set of three linear guide grooves16 c which extend parallel to the optical axis O. The inner ring 17 isprovided on the thick-wall cylinder portion 17 a with a set of threelinear guide keys 17 b which extend radially outwards to be slidablyengaged in the set of three linear guide grooves 16 c of the main ringbody 16 r, respectively. The outer ring 16 is provided at the rear endthereof with a set of three bayonet prongs 16 d (only one of whichappears in FIG. 5) which extend radially inwards. The cam ring 15 isprovided, in the vicinity of the rear end thereof immediately in frontof the thick-wall cylinder portion 15 a, with a circumferential groove15 c in which the set of three bayonet prongs 16 d are engaged to bemovable in the circumferential groove 15 c within a predetermined angleof rotation. When the cam ring 15 is positioned within an operatingangle relative to the outer ring 16, the cam ring 15 and the outer ring16 are movable together in the optical axis direction withoutdisengaging from each other, and at the same time, the cam ring 15 isrotatable about the optical axis O relative to the outer ring 16 due tothe engagement of the set of three bayonet prongs 16 d with thecircumferential groove 15 c.

The main ring body 17 r of the inner ring 17 is provided in the vicinityof the front end thereof with an inner flange 17 c which extendsradially inwards and to which a barrier unit 40 and the barrier drivering 31 are fixed. The main ring body 17 r of the inner ring 17 isprovided, on an rear face of the inner flange 17 c at equi-angularintervals in a circumferential direction of the inner ring 17, with theset of three linear guide bosses 17 d (only one of which appears inFIGS. 1 and 3). The zoom lens barrel 1 is provided with the first lensgroup moving frame 18 which is provided in the inner ring 17. The firstlens group moving frame 18 is provided at the front end thereof with aninner flange 18 b which extends radially inwards to form a circularaperture having the center thereof about the optical axis O. A femalethread portion 18 d is formed on an inner peripheral face of the innerflange 18 b. The first lens group moving frame 18 is provided on theinner flange 18 b with the set of three linear guide holes 18 a in whichthe set of three linear guide bosses 17 d of the inner ring 17 areslidably engaged, respectively. Each linear guide hole 18 a is formedhaving an oval cross section which is elongated in a radial direction ofthe first lens group moving frame 18. Even if each linear guide boss 17d is fitted in the associated linear guide hole 18 a with a substantialclearance therebetween, the inner ring 17 is guided in the optical axisdirection relative to the first lens group moving frame 18 with asufficient degree of precision since the first lens group moving frame18 is slidably fitted into the cam ring 15. The first lens group movingframe 18 is provided, on an inner peripheral surface thereof atequi-angular intervals in a circumferential direction thereof, with theset of three linear guide grooves 18 c which extend parallel to theoptical axis O.

The second lens group moving frame 19 is fitted in the first lens groupmoving frame 18. The second lens group moving frame 19 is provided, onan outer peripheral surface thereof at the front end of the outerperipheral surface, with the set of three linear guide keys 19 a whichare slidably engaged into the set of three linear guide grooves 18 c ofthe first lens group moving frame 18, respectively.

As shown in FIGS. 5, 6 and 7, the second lens group L2 includes threelens elements: front, middle and rear lens elements. The front lenselement is fixed to the second lens group moving frame 19 to be directlysupported thereby. The rear lens element is supported by a support ring19 d which is fixed to the second lens group moving frame 19 from rearthereof, so that the rear lens element is supported by the second lensgroup moving frame 19 via the support ring 19 d. The middle lens elementis fixed to the rear lens element so that a rear surface of the middlelens element is cemented to a front surface of the rear lens element.Accordingly, the middle lens element of the second lens group L2 issupported by the second lens group moving frame 19 via the rear lenselement of the second lens group L2 and the support ring 19 d.

As can be understood from the above description, according to the abovedescribed guiding mechanisms of the zoom lens barrel 1, the outer ring16 is guided linearly in the optical axis direction without rotatingabout the optical axis O via the stationary ring 13, the inner ring 17is guided linearly in the optical axis direction without rotating aboutthe optical axis O via the outer ring 16, the first lens group movingframe 18 is guided linearly in the optical axis direction withoutrotating about the optical axis O via the inner ring 17, and the secondlens group moving frame 19 is guided linearly in the optical axisdirection without rotating about the optical axis O via the first lensgroup moving frame 18, in that order from the outside to the inside ofthe zoom lens barrel 1.

Furthermore, the linear guiding mechanism provided between the innerring 17 and the first lens group moving frame 18 includes the set ofthree linear guide bosses 17 d, which extend in a direction parallel tothe optical axis, and the set of three linear guide holes 18 a, and ispositioned in the vicinity of the front end of each of the inner ring 17and the first lens group moving frame 18. Due to this structure, noother linear guiding elements have to be provided on either the insideor the outside of the cam ring 15. This contributes to a reduction ofthe annular space between the inner ring 17 and the first lens groupmoving frame 18 to thereby minimize the diameter of the zoom lens barrel1.

As shown in FIGS. 5 through 7, the zoom lens barrel 1 is provided with afirst lens frame (lens supporting frame) 20 to which the first lensgroup L1 is fixed. The first lens frame 20 is fixed to the first lensgroup moving frame 18, so that the first lens frame 20 and the firstlens group moving frame 18 constitute a front lens support member.Accordingly, the first lens group L1 is supported by the first lensgroup moving frame 18 via the first lens frame 20. More specifically,the first lens frame 20 is provided on an outer peripheral surfacethereof with a male thread portion which is in mesh with the femalethread portion 18 d of the inner flange 18 b. The first lens frame 20 iscemented to the first lens group moving frame 18 by an adhesive afterthe thread engagement position of the male thread portion of the firstlens frame 20 with respect to the female thread portion 18 d of theinner flange 18 b has been adjusted during assembly. The zoom lensbarrel 1 is provided in an annular recess 19 b of the second lens groupmoving frame 19 with a shutter unit 21 which is fixed to the second lensgroup moving frame 19 by set screws (not shown). A light shield ring 19c is fitted in the second lens group moving frame 19 from front thereofto be fixed thereto to hold the shutter unit 21 between the light shieldring 19 c and the second lens group moving frame 19. The shutter unit 21is provided with shutter blades 21 a. The shutter unit 21 drives theshutter blades 21 a to open and close in accordance with information onan object brightness. The zoom lens barrel 1 is provided therein with aflexible printed wiring board (flexible PWB) 21 b one end (front end) ofwhich is fixed to the shutter unit 21 (see FIG. 7). A drive signal isgiven to the shutter unit 21 via the flexible PWB 21 b. As shown in FIG.7, the flexible PWB 21 b extends rearward from the shutter unit 21, andsubsequently bends radially outwards to extend forward. Subsequently,the flexible PWB 21 b penetrates the stationary ring 13 via athrough-slot 28 a (see FIGS. 4 and 7) formed thereon, and bends radiallyoutwards to extend rearward along a guiding portion 28 of the stationaryring 13 which extends parallel to the optical axis O. A portion of theflexible PWB 21 b which extends along the outer surface of the guidingportion 28 is cemented thereto. Subsequently, the flexible PWB 21 bextends rearward to be positioned outside the housing 11. As shown inFIG. 7, a bending portion 21 bx of the flexible PWB 21 b in the vicinityof the through-slot 28 a passes through a rubber band 29 which is hookedover a hook 11 f formed at the rear end of the housing 11. In a statewhere the zoom lens barrel 1 is fully extended as shown below theoptical axis O in FIG. 7, the front end of the stretched rubber band 29is positioned behind the position of the through-slot 28 a in theoptical axis direction to pull the bending portion 21 bx obliquelyrearwards in a direction away from the optical axis O to prevent theflexible PWB 21 b from bending to interfere with the photographingoptical path of the zoom lens barrel 1.

The zoom lens barrel 1 is provided with a third lens frame 22 to whichthe third lens group L3 is fixed. As shown in FIG. 4, the third lensframe 22 is guided in the optical axis direction via a pair of linearguide rods 22 a which extend parallel to the optical axis. The front andrear ends of each linear guide rod 22 a are fixed to the shaft holdingmember 12 and the housing 11, respectively. The third lens frame 22 isdriven to move in the optical axis direction by rotation of a feed screw24 which is driven forwardly and reversely by a step motor (not shown)in accordance with information on a photographing distance.

A zooming operation is carried out by moving the first and second lensgroups L1 and L2 (the first and second lens group moving frames 18 and19) in the optical axis direction relative to the third lens group L3while varying the distance therebetween. The cam ring 15 is provided, onan inner peripheral surface thereof at equi-intervals in acircumferential direction of the cam ring 15, with a set of threelens-drive cam grooves C1 (see FIGS. 1, 3 and 5). The first lens groupmoving frame 18 and the second lens group moving frame 19, which areguided linearly in the optical axis direction without rotating about theoptical axis O, move in the optical axis direction by rotation of thecam ring 15 in accordance with the profiles of the lens-drive camgrooves C1. The developed view of the lens-drive cam grooves C1 is shownin FIGS. 8 through 10. In FIG. 8 each lens-drive cam groove C1, which isformed on an inner peripheral surface of the cam ring 15, is shown bydotted lines and is shown by solid lines in FIGS. 9 and 10 to clearlyindicate the profile thereof. A feature of the zoom lens barrel 1 isthat each lens-drive cam groove C1 is formed as a continuous bottomedgroove to have respective cam groove portions for the first and secondlens groups L1 and L2, and that the first and second lens groups L1 andL2 are released from the constraints of the set of three lens-drive camgrooves C1 at their respective accommodation positions so that the firstand second lens groups L1 and L2 can be accommodated to be positionedclose to each other until the first lens frame 20 and the second lensgroup moving frame 19 come into contact with each other.

Namely, the set of three follower pins 18 f that are projected radiallyoutwards from the first lens group moving frame 18 and the set of threefollower pins 19 f that are projected radially outwards from the secondlens group moving frame 19 are slidably engaged in the set of threelens-drive cam grooves C1, respectively. Each lens-drive cam groove C1,which is formed as a continuous bottomed groove, has a function to movethe first and second lens groups L1 and L2 (the first and second lensgroup moving frames 18 and 19) in their respective zoom paths. Unlikethe present embodiment of the zoom lens barrel 1, in a conventional zoomlens barrel having a cam ring for driving a plurality of movable lensgroups, a set of cam grooves is necessary for each of the plurality ofmovable lens groups.

Each lens-drive cam groove C1 is provided at one end thereof with aninsertion end C1 e via which one of the three follower pins 18 f of thefirst lens group moving frame 18 and one of the three follower pins 19 fof the second lens group moving frame 19 are inserted into thelens-drive cam groove C1. Each lens-drive cam groove C1 is furtherprovided with a first-lens-group zooming section (first moving section)C1Z1, a second-lens-group zooming section (second moving section) C1Z2,a first-lens-group accommodation section C1A1 and a second-lens-groupaccommodation section C1A2, in that order from the insertion end C1 e.The opposite ends (lower and upper ends as viewed in FIG. 9) of thefirst-lens-group zooming section C1Z1 determines a telephoto extremityZ1T and a wide-angle extremity Z1W of the first lens group L1,respectively. The opposite ends (lower and upper ends as viewed in FIG.9) of the second-lens-group zooming section C1Z2 determines a telephotoextremity Z2T and a wide-angle extremity Z2W of the second lens groupL2, respectively. As shown in FIGS. 8 through 10, the width of each ofthe first-lens-group accommodation section C1A1 and thesecond-lens-group accommodation section C1A2 in the optical axisdirection is greater than the width of each the first-lens-group zoomingsection C1Z1 and the second-lens-group zooming section C1Z2 so that theassociated follower pins 18 f and 19 f can move freely in thefirst-lens-group accommodation section C1A1 and the second-lens-groupaccommodation section C1A2, respectively. Namely, the first-lens-groupaccommodation section C1A1 extends in a circumferential direction of thecam ring 15, and also widens in the optical axis direction to form aclearance for the associated follower pin 18 f of the first lens groupmoving frame 18 to be movable in the optical axis direction by an amountof movement corresponding to the range of adjustment of the threadengagement position of the male thread portion of the first lens frame20 with respect to the female thread portion 18 d of the inner flange 18b. On the other hand, the second-lens-group accommodation section C1A2extends in both a circumferential direction of the cam ring 15 and theoptical axis direction to form a substantially triangular area to form aclearance for the associated follower pin 19 f of the second lens groupmoving frame 19 to be movable freely and widely in both thecircumferential direction of the cam ring 15 and the optical axisdirection within the triangular area.

The relative angular positions of the set of three follower pins 18 fand the set of three follower pins 19 f about the optical axis O aredetermined so that each follower pin 18 f and each follower pin 19 f arerespectively positioned in the first-lens-group accommodation sectionC1A1 and the second-lens-group accommodation section C1A2 when the camring 15 is positioned in an accommodation position thereof. Thefirst-lens-group accommodation section C1A1 and the second-lens-groupaccommodation section C1A2, to some extent, do not constrain movement ofthe associated follower pins 18 f and 19 f, respectively. Namely, eachfollower pin 18 f and each follower pin 19 f can move in thefirst-lens-group accommodation section C1A1 and the second-lens-groupaccommodation section C1A2, respectively, in the optical axis directionbecause of the clearance formed between each groove portion and theassociated follower pin. This clearance contributes to furtherminiaturization of the length of the zoom lens barrel 1 in anaccommodation state thereof (i.e., the distance between the first lensgroup moving frame 18 and the second lens group moving frame 19 in theoptical axis direction can be minimized since both moving frames 18 and19 are released from positioning restrictions of the cam grooves and camfollowers thereof). The amount of clearance formed between thefirst-lens-group accommodation section C1A1 and the associated followerpin 18 f is sufficient to absorb a variation in position of theassociated follower pin 18 f which is caused by an adjustment of thethread engagement position of the male thread portion of the first lensframe 20 with respect to the female thread portion 18 d of the innerflange 18 b in an accommodation state of the zoom lens barrel 1.

The inner flange 17 c of the inner ring 17 is provided with a set ofthree engaging protrusions 17 g (only one of which appears in FIGS. 1, 3and 5) arranged at different angular positions in a circumferentialdirection of the inner ring 17. The first lens group moving frame 18 isprovided with a set of three recesses 18 g to correspond to the set ofthree engaging protrusions 17 g. Three helical compression springs 30serving as a biasing device are inserted to be held between the set ofthree engaging protrusions 17 g and the set of three recesses 18 g,respectively, to press the first lens group moving frame 18 rearwards inthe optical axis direction. Therefore, the first lens frame 20, which issupported by the first lens group moving frame 18, can retract up to amechanical contacting point P (see FIGS. 5 and 6) where the first lensframe 20 comes in contact with the light shield ring 19 c of the secondlens group moving frame 19 due to the clearance between thefirst-lens-group accommodation section C1A1 of each lens-drive camgroove C1 of the cam ring 15 and the associated follower pin 18 f of thefirst lens group moving frame 18. By providing the helical compressionsprings 30, which have a small length, in between the inner ring 17 andthe first lens group moving frame 18, the relative movement between thefirst and second lens group moving frames 18 and 19 can be reduced,however, even if the helicoid compression springs 30 are not provided,the first and second lens group moving frames 18 and 19 can stillretract up so that the first lens frame 20 contacts the mechanicalcontacting point P. Likewise, the second lens group moving frame 19 canretract up to a mechanically contacting point Q (see FIGS. 5 and 6)where the second lens group moving frame 19 comes in contact with thethird lens frame 22 due to a clearance between the second-lens-groupaccommodation section C1A2 of each lens-drive cam groove C1 of the camring 15 and the associated follower pin 19 f of the second lens groupmoving frame 19. Due to such structures of the mechanical contactingpoints P and Q, the length of the zoom lens barrel 1 in an accommodationstate thereof is successfully reduced as compared with a conventionalzoom lens barrel in which the respective accommodation positions offirst and second lens groups which correspond to the first and secondlens groups L1 and L2 of the present embodiment of the zoom lens barrelare precisely determined by associated cam grooves. Furthermore, thethird lens frame 22 can retract up to a mechanical contacting point Rwhere it comes in contact with the housing 11 while compressing ahelical compression spring 23 (see FIGS. 1 and 4), which is positionedbetween the third lens frame 22 and the housing 11 to press the thirdlens frame 22, forward. The axial cross sectional view of the zoom lensbarrel 1 above the optical axis O in each of FIGS. 5, 6 and 7 shows anaccommodation state of the zoom lens barrel 1 where the first lens frame20 is in contact with the light shield ring 19 c of the second lensgroup moving frame 19, where the second lens group moving frame 19 is incontact with the third lens frame 22, and where the third lens frame 22is in contact with the housing 11. The amount of rearward movement ofthe first lens group moving frame 18 relative to the second lens groupmoving frame 19 depends on the position of the first lens frame 20relative to the first lens group moving frame 18 because the position ofthe first lens frame 20 relative to the first lens group moving frame 18varies by an adjustment of the thread engagement position of the malethread portion of the first lens frame 20 with respect to the femalethread portion 18 d of the inner flange 18 b during assembly. Such avariation due to the adjustment is absorbed by extension or compressionof the helical compression springs 30 so that the zoom lens barrel 1 canbe accommodated with the first lens frame 20, the second lens groupmoving frame 19 and the third lens frame 22 being in contact with thelight shield ring 19 c, the third lens frame 22 and the housing 11 atthe mechanically contacting points P, Q and R, respectively.

If the cam ring 15 rotates in a direction from the accommodationposition toward a ready-to-photograph position in a zooming sectionbetween the telephoto extremity Z1T and the wide-angle extremity Z1Wthereof, each follower pin 18 f of the first lens group moving frame 18which is engaged in the first-lens-group accommodation section C1A1moves from the first-lens-group accommodation section C1A1 to thefirst-lens-group zooming section C1Z1 via the second-lens-group zoomingsection C1Z2, while each follower pin 19 f of the second lens groupmoving frame 19 which is engaged in the second-lens-group accommodationsection C1A2 moves from the second-lens-group accommodation section C1A2to the second-lens-group zooming section C1Z2 via the first-lens-groupaccommodation section C1A1. Accordingly, the second-lens-group zoomingsections C1Z2 of the set of three lens-drive cam grooves C1 that areused for driving the set of three follower pins 19 f of the second lensgroup moving frame 19 are used as mere passing sections for the set ofthree follower pins 18 f of the first lens group moving frame 18 viawhich the set of three follower pins 18 f move from the first-lens-groupaccommodation position to the ready-to-photograph position. Theabove-described structure which provides such passing sections isadvantageous to reduce the number of cam grooves which are to be formedon the cam ring 15, which is in turn advantageous to reduce the angle ofinclination of each cam groove with respect to a circumferentialdirection of the cam ring 15.

The inner ring 17 moves in the optical axis direction independent of thefirst lens group moving frame 18 in a moving path which is substantiallyidentical to the moving path of the first lens group moving frame 18.Accordingly, the cam ring 15 is provided, on an outer peripheral surfaceat equi-intervals in a circumferential direction thereof, with a set ofthree cam grooves C2. The inner ring 17 is provided, on an innerperipheral surface at equi-intervals in a circumferential directionthereof, with a set of three follower pins 17 f (only one of themappears in FIG. 5) which are slidably engaged in the set of three camgrooves C2 of the cam ring 15, respectively. As can be seen in FIG. 8,the profiles of the cam grooves C2 resemble those of the lens-drive camgrooves C1. As shown in FIG. 8, each cam groove C2 is provided at oneend thereof with an insertion end C2 e via which one of the threefollower pins 17 f of the inner ring 17 is inserted into the cam grooveC2. Each cam groove C2 is further provided with a first section C2Z1which corresponds to the first-lens-group zooming section C1Z1, a secondsection C2Z2 which corresponds to the second-lens-group zooming sectionC1Z2, and a barrier drive section C2B. The barrier drive section C2Bextends in a circumferential direction of the cam ring 15, so that thecam ring 15 rotates about the optical axis O without moving in theoptical axis direction relative to the inner ring 17 as long as eachfollower pin 17 f is engaged in the barrier drive section C2B. As can beclearly seen in FIG. 8, the set of three lens-drive cam grooves C1 andthe set of three cam grooves C2 are formed on the cam ring 15 atslightly different positions in the optical axis direction, while theset of three follower pins 17 f that are respectively engaged in the setof three cam grooves C2 and the set of three follower pins 18 f that arerespectively engaged in the set of three lens-drive cam grooves C1 arerespectively aligned side by side in a direction parallel to the opticalaxis O.

By providing the inner ring 17, which extends forward so that an outerperipheral surface thereof is exposed to the outside of the zoom lensbarrel 1, as an element separate from the first lens group moving frame18, and by guiding the inner ring 17 in the optical axis direction via acam mechanism independent of the first lens group moving frame 18 asdescribed above, external forces applied to the inner ring 17 can beprevented from being transferred to the first lens group L1 via thefirst lens group moving frame 18, which in turn prevents deteriorationin optical performance of the zoom lens barrel 1 due to eccentricity ofthe optical axis of the first lens group L1. In addition, the structureof the cam ring 15 wherein the set of three lens-drive cam grooves C1and the set of three cam grooves C2, whose cam profiles are similar(though differing slightly in shape) Fall to each other, are formed onthe cam ring 15 in slightly different positions thereon in the opticalaxis direction does not increase the wall thickness of the cam ring 15;moreover, external forces applied to the inner ring 17 in a directionradially inwards can be received by the first lens group moving frame 18via the set of three follower pins 18 f (i.e. the strength of the wholezoom lens barrel 1 can be reinforced). Furthermore, since the set ofthree follower pins 17 f and the set of three follower pins 18 f arerespectively aligned side by side in a direction parallel to the opticalaxis O, the strength of the spring force of the three helicalcompression springs 30 that are held between the inner ring 17 and thefirst lens group moving frame 18 to bias the inner ring 17 and the firstlens group moving frame 18 in opposite directions away from each othervaries little even if the cam ring 15 rotates relative to the inner ring17 and the first lens group moving frame 18. Namely, since the directionof the helical compression springs 30 and aligned direction of the camfollowers 17 f and 18 f are same and are parallel to the optical axis O,backlash with the cam grooves C1 and the cam followers 17 f and backlashwith the cam grooves C2 and cam followers 18 f are absorbed by thehelical compression springs 30, and accordingly, the optical performanceof the zoom lens can be reliably maintained wherever the cam followers17 f and 18 f are positioned in the cam-grooves C1 and C2 respectively.

The barrier unit 40 is fixed to an inner surface of the main ring body17 r to be positioned therein. The barrier drive ring 31 is positionedin the inner ring 17 and held between the barrier unit 40 and the innerflange 17 c of the inner ring 17 to be rotatable freely about theoptical axis O. The cam ring 15 is provided at the front end thereofwith a set of three recesses 15 k. The barrier drive ring 31 is providedon an outer peripheral surface thereof with a set of three engagingportions 31 a. The cam ring 15 is provided at one end (upper end asviewed in FIG. 8) of each recesses 15 k with a rotation transfer face 15d which extends parallel to the optical axis O and extends through acorresponding opening 17 z (see FIG. 7) provided on a circumferentialportion of the inner flange 17 c. If the cam ring 15 rotates about theoptical axis O in a barrier closing direction (clockwise as viewed fromthe front of the zoom lens barrel 1) with respect to the inner ring 17with the set of three follower pins 17 f being respectively engagedwithin the barrier drive sections C2B of the set of three cam grooves C2of the cam ring 15, the three rotation transfer faces 15 d firstly comeinto contact with the three engaging portions 31 a of the barrier drivering 31 and subsequently press the three engaging portions 31 a to givea rotational force to the barrier drive ring 31 to close a pair ofbarrier blades 42, respectively. As shown in FIG. 8, the set of threerecesses 15 k are formed on the cam ring 15 at portions thereon otherthan the portions where the three lens-drive cam grooves C1 and thethree cam grooves C2 are formed.

As shown in FIGS. 2 and 14, the barrier unit 40 is provided with abarrier blade support front plate 41, the pair of barrier blades 42, twotorsion springs 43 and a barrier blade support rear plate 44, and isformed as a single assembly in advance. The barrier blade support frontplate 41 is provided at the center thereof with a substantiallyrectangular photographing aperture 41 a, and is further provided, on anrear surface thereof on opposite sides of the photographing aperture 41a, with two bosses 41 b, respectively, which extend rearwards. Eachbarrier blade 42 is provided at one end thereof with a hole in which oneof the two bosses 41 b is engaged so that each barrier blade 42 isrotatable about the associated boss 41 b. The two torsion springs 43bias the pair of barrier blades 42 to rotate in opposite rotationaldirections to shut the pair of barrier blades 42, respectively. The pairof barrier blades 42 are supported between the barrier blade supportfront plate 41 and the barrier blade support rear plate 44. The barrierblade support rear plate 44 is provided at the center thereof with acentral aperture 44 b (see FIG. 2) thereof which is aligned with thephotographing aperture 41 a in the optical axis direction, and isfurther provided on opposite sides of the central aperture with twoslots 44 a. As shown in FIGS. 12 and 13, each barrier blade 42 isprovided in the vicinity of the associated boss 41 b with an engagingprojection 42 a which extends rearward, toward the barrier drive ring31, to pass through the associated slot 44 a of the barrier bladesupport rear plate 44. The barrier drive ring 31 is provided on left andright sides of a central opening thereof with two drive projections 31 cwhich are respectively engaged with the two engaging projections 42 a ofthe pair of barrier blades 42. FIG. 12 shows the pair of barrier blades42 with chain lines in a closed state thereof, and FIG. 13 shows thepair of barrier blades 42 with chain lines in a fully open statethereof. FIG. 14 shows fundamental elements of the barrier unit 40 withthe barrier blade support front plate 41 removed.

The barrier drive ring 31 is biased to rotate in a direction to open thepair of barrier blades 42 by a helical extension spring 45 whoseopposite ends are hooked on an engaging projection 31 b formed on thebarrier drive ring 31 and an engaging projection 17 h formed on a frontsurface of the inner flange 17 c of the inner ring 17. The spring forceof the helical extension spring 45 is greater than the total springforce of the two torsion springs 43. The two drive projections 31 c ofthe barrier drive ring 31 come into contact with the two engagingprojections 42 a of the pair of barrier blades 42 to open the pair ofbarrier blades 42, respectively, when the barrier drive ring 31 is in afully rotated position thereof by the spring force of the helicalextension spring 45 (see FIG. 13). If the barrier drive ring 31 isrotated in a direction to close the pair of barrier blades 42 againstthe spring force of the helical extension spring 45, the two driveprojections 31 c respectively move away from the two engagingprojections 42 a of the pair of barrier blades 42 so that the pair ofbarrier blades 42 are closed by the spring force of the two torsionsprings 43 (see FIG. 12).

The three rotation transfer faces 15 d of the cam ring 15 respectivelycome into contact with the three engaging portions 31 a of the barrierdrive ring 31 to press the three engaging portions 31 a against thespring force of the helical extension spring 45 to rotate the barrierdrive ring 31. When the cam ring 15 is in the accommodation positionthereof, the three rotation transfer faces 15 d are respectively incontact with the three engaging portions 31 a of the barrier drive ring31 via three through-slots 17 z formed on the inner flange 17 c of theinner ring 17. The barrier drive ring 31 is rotated about the opticalaxis O against the spring force of the helical extension spring 45 toclose the pair of barrier blades 42. If the cam ring 15 rotates aboutthe optical axis O in a barrier opening direction (counterclockwise asviewed from the front of the zoom lens barrel 1) with respect to theinner ring 17 with the set of three follower pins 17 f beingrespectively engaged within the barrier drive sections C2B of the set ofthree cam grooves C2 of the cam ring 15, the three rotation transferfaces 15 d are respectively disengaged from the three engaging portions31 a of the barrier drive ring 31 so that the barrier drive ring 31 isrotated in a direction to open the pair of barrier blades 42 by thespring force of the helical extension spring 45.

FIG. 16 shows the movement of the three rotation transfer faces 15 d ofthe cam ring 15 in the case where the cam ring 15 rotates so that eachfollower pin 15 b, which is engaged in the associated cam slot 13 b ofthe stationary ring 13, moves from the linear slot portion 13 b 1 to thestate-changing slot portion 13 b 2 of the associated cam slot 13 b,i.e., from the accommodation position to the preparation section (seeFIG. 11). Due to the engagement of the set of three follower pins 15 bof the cam ring 15 with the set of three cam slots 13 b and the set ofthree rotation transfer grooves 14 a, the cam ring 15 firstly rotatesabout the optical axis O while moving in the optical axis direction(each rotation transfer face 15 d moves from a position “1—1” to aposition “4—4” via positions “2—2” and “3—3” in FIG. 16), andsubsequently rotates about the optical axis O without moving in theoptical axis direction (each rotation transfer face 15 d moves from theposition “4—4” to a position “5—5” in FIG. 16). When moving from theposition “4—4” to the position “5—5”, the three rotation transfer faces15 d of the cam ring 15 are respectively disengaged from the threeengaging portions 31 a of the barrier drive ring 31 to thereby open thepair of barrier blades 42 by the spring force of the helical extensionspring 45. Conversely, if the cam ring 15 rotates so that each followerpin 15 b moves from the preparation section to the accommodationposition, the movement of each rotation transfer face 15 d from theposition “5—5” to the position “4—4” causes the pair of barrier blades42 to close.

Each of the pair of barrier blades 42 is formed as a substantially planeplate, and is provided on a rear face thereof with a semi-circularconcave face 42 b (see FIGS. 5, 6 and 17) so that the rear face of eachbarrier blade 42 does not come in contact with a frontmost surface(convex surface) L1 r of the first lens group L1. The two semi-circularconcave faces 42 b together form a circular concave face the shape ofwhich corresponds to the shape of a central portion of the convexfrontmost surface L1 r of the first lens group L1 in a state where thepair of barrier blades 42 are closed. The curvature of eachsemi-circular concave face 42 b is determined to corresponds to thecurvature of the frontmost surface L1 r of the first lens group L1. Theconcave faces 42 b of the pair of barrier blades 42 make it possible toretreat the inner ring 17 to a rearward limit when the inner ring 17 isaccommodated. The concave face 42 b is formed on each barrier blade 42when the barrier blades 42 are molded of synthetic resin.

After the reinforcing ring 17 x is fitted on and adhered to the mainring body 17 r, the barrier unit 40 having the above described structureis fitted into the reinforcing ring 17 x from the front thereof. Thebarrier blade support front plate 41 is provided on an outer peripheraledge thereof with a plurality of engaging portions which arerespectively engaged with a corresponding plurality of hooks formed onan inner peripheral surface of the main ring body 17 r in front of theinner flange 17 c to prevent the barrier unit 40 from coming off thefront of the inner ring 17. The barrier drive ring 31 is held betweenthe barrier unit 40 and the inner flange 17 c of the inner ring 17 to berotatable about the optical axis O. The main ring body 17 r, which ismade of synthetic resin, is provided, at the front end thereof onopposite sides of the central circular opening of the main ring body 17r, with two cutout portions 17 k (see FIG. 14) in which respective outeredges of the pair of barrier blades 42 enter when the pair of barrierblades 42 are fully opened as shown in FIG. 14. The radially outer endsof the two cutout portions 17 k are fully covered by the reinforcingring 17 x. The main body ring 17 r can be provided with the two cutoutportions 17 k each formed as a through hole in a radial direction of theinner ring 17 due to the structure wherein the inner ring 17 isconstructed from two separate elements: the synthetic-resin-made mainbody ring 17 r and the metal reinforcing ring 17 x. Conventionally, if aset of barrier blades such as the pair of barrier blades 42 of the zoomlens barrel 1 is designed to consist of four blades, the total thicknessof the four blades in the optical axis direction increases though theradial width of each blade is reduced. Conversely, if the set of barrierblades is designed to consist of one or two barrier blades, though thetotal thickness of the blade or blades in the optical axis direction isreduced, the radial width of each blade increases. However, in thepresent embodiment of the zoom lens barrel 1, the formation of the twocutout portions 17 k on the main body ring 17 r that serve as recessesfor the pair of barrier blades 42 contributes to further miniaturizationof the diameter of the inner ring 17 without increasing the totalthickness of the barrier blades 42 in the optical axis direction.

As has been described above, the zooming slot portion 13 b 3 of each camslot 13 b of the stationary ring 13 extends in a circumferentialdirection of the stationary ring 13 and does not extend in the opticalaxis direction. Therefore, the set of three follower pins 15 b of thecam ring 15 rotate about the optical axis O without moving in theoptical axis direction when following the zooming slot portions 13 b 3of the set of three cam slots 13 b in the zooming section (see FIG. 11).The zoom lens barrel 1 is provided between the housing 11 and therotatable ring 14 with a biasing ring 32 which is fitted on a front partof the rotatable ring 14 to remove backlash and play between the set ofthree follower pins 15 b and the zooming slot portions 13 b 3 of the setof three cam slots 13 b. The biasing ring 32 and the rotatable ring 14are provided with three hooks 32 a and corresponding three hooks 14 c,respectively. Opposite ends of three helical extension springs 33 arehooked on the three hooks 32 a and the three hooks 14 c, respectively,to constantly bias the biasing ring 32 rearwards in the optical axisdirection. The biasing ring 32 is provided, on an inner peripheralsurface thereof at equi-angular intervals in a circumferential directionof the biasing ring 32, with a set of three inward projections 32 cwhich extend radially inwards, while the rotatable ring 14 is providedin the vicinity of the front end thereof with a corresponding set ofthree through-slots 14 d which extend parallel to the optical axis O sothat the set of three inward projections 32 c penetrate the rotatablering 14 via the set of three through-slots 14 d in radially inwarddirections, respectively. The set of three through-slots 14 d are formedon the rotatable ring 14 so as to be communicatively connected in frontportions of the set of three rotation transfer grooves 14 a to penetratetherethrough, so that the set of three inward projections 32 c arepositioned in front of the set of three follower pins 15 b that areengaged in the set of three rotation transfer grooves 14 a,respectively. If each follower pin 15 b of the cam ring 15 moves fromthe state-changing slot portion 13 b 2 to the zooming slot portion 13 b3, respective rear faces of the set of three inward projections 32 ccome into pressing contact with the set of three follower pins 15 b topress each follower pin 15 b rearward in the optical axis directionagainst the rear side edge of the associated zooming slot portion 13 b 3to thereby remove backlash and play between the set of three followerpins 15 b and the zooming slot portions 13 b 3 of the set of three camslots 13 b.

In addition to the above described structures wherein the set of threelinear guide grooves 18 c are formed on an inner peripheral surface ofthe first lens group moving frame 18 while the set of three linear guidekeys 19 a, which are respectively engaged in the set of three linearguide grooves 18 c, are formed on an outer peripheral surface of thesecond lens group moving frame 19, the aforementioned set of threecircumferential recesses 18 h are formed on the first lens group movingframe 18 at the front ends of the set of three linear guide grooves 18c, respectively. Each circumferential recess 18 h allows the associatedlinear guide key 19 a of the second lens group moving frame 19 to movetherein in a circumferential direction about the optical axis O, i.e.,allows the second lens group moving frame 19 to rotate about the opticalaxis O relative to the first lens group moving frame 18 in a rangecorresponding to the circumferential length of the circumferentialrecess 18 h. The second lens group moving frame 19 can rotate about theoptical axis O relative to the first lens group moving frame 18 alongthe three circumferential recesses 18 h only when the second lens groupmoving frame 19 is in the vicinity of the accommodation positionthereof. The first lens group moving frame 18 is provided on the innerflange 18 b thereof with a set of three circumferential slots 18 j (seeFIGS. 3 and 6). The second lens group moving frame 19 is provided at thefront end thereof with a set of three front projecting portions 19 e onrespective outer surfaces of which the three linear guide keys 19 a areformed, respectively. When each linear guide key 19 a is positioned inthe associated circumferential recess 18 h, i.e., when the second lensgroup L2 is in the vicinity of the accommodation position thereof, theset of three front projecting portions 19 e of the second lens groupmoving frame 19 penetrate through (extend through) the inner flange 18 bof the first lens group moving frame 18 to project forward from theinner flange 18 b via the set of three circumferential slots 18 j,respectively. Accordingly, by allowing the three linear guide keys 19 ato project forward from the inner flange 18 b through the threecircumferential slots 18 j, respectively, the length in the optical axisdirection of the three linear guide grooves 18 c and the circumferentialrecesses 18 h which reliably carry out the engaging and disengaging ofthe three linear guide keys 19 a with the three linear guide grooves 18c, and the amount of movement of the first and second lens group movingframes 18 and 19 in the optical axis direction can be maintained withoutincreasing the combined length of the first and second lens group movingframes 18 and 19 at the accommodation positions thereof. At this time,the three linear guide keys 19 a are loosely fitted in the threecircumferential slots 18 j. The reason why the second lens group movingframe 19 is allowed to rotate relative to the first lens group movingframe 18 along the three circumferential recesses 18 h only when thesecond lens group moving frame 19 is in the vicinity of theaccommodation position thereof will be hereinafter discussed.

In a state where the zoom lens barrel 1 is in an accommodation state,i.e., where each of the set of three follower pins 18 f of the firstlens group moving frame 18 is engaged in the first-lens-groupaccommodation section C1A1 of the associated lens-drive cam groove C1, arotation of the cam ring 15 in a direction to extend the zoom lensbarrel 1 (in a direction indicated by an arrow “X” in FIG. 10, i.e.,counterclockwise as viewed from the front of the zoom lens barrel 1)causes each follower pin 18 f of the first lens group moving frame 18 tomove from the first-lens-group accommodation section C1A1 to thesecond-lens-group zooming section C1Z2 of the associated lens-drive camgroove C1, to thereby cause the first lens group moving frame 18 to moveforward in the optical axis direction. Such a movement of each followerpin 18 f of the first lens group moving frame 18 is indicated stepwiseby first, second, third and fourth positions “1 a”, “2 a”, “3 a” and “4a” in FIG. 10. Likewise, the corresponding movement of each follower pin19 f of the second lens group moving frame 19 is indicated stepwise byfirst, second, third and fourth positions “1 b”, “2 b”, “3 b” and “4 b”in FIG. 10, while the corresponding movement of each linear guide key 19a of the second lens group moving frame 19 is indicated stepwise byfirst, second, third and fourth positions “1 c”, “2 c”, “3 c” and “4 c”in FIG. 10.

In addition, such a rotation of the cam ring 15 in the direction X shownin FIG. 10 causes each follower pin 19 f of the second lens group movingframe 19 which is positioned in the second-lens-group accommodationsection C1A2 of the associated lens-drive cam groove C1 to move from theposition “1 b” to the position “2 b” in the second-lens-groupaccommodation section C1A2 to come into contact with a surface XX of aninclined side edge β of the second-lens-group accommodation section C1A2which is inclined with respect to a circumferential direction of the camring 15. The position “2 b” in the second-lens-group accommodationsection C1A2 is positioned on the inclined side edge β of thesecond-lens-group accommodation section C1A2.

A further rotational movement of the cam ring 15 in the same direction Xcauses each follower pin 19 f of the second lens group moving frame 19to slide on the surface XX of the inclined side edge β in a directioninclined to both the optical axis direction and the circumferentialdirection of the cam ring 15 in a manner such as the following.

At this time, each linear guide key 19 a is in contact with a sidesurface (the lower surface as viewed in FIG. 10) of the associatedcircumferential recess 18 h of the first lens group moving frame 18 (seethe position “2 c” of the linear guide key 19 a shown in FIG. 10).Therefore, a forward movement of the first lens group moving frame 18 inthe optical axis direction causes the first lens group moving frame 18to push the second lens group moving frame 19 forward in the opticalaxis direction via the circumferential recesses 18 h and the set ofthree linear guide keys 19 a, and at the same time, causes the secondlens group moving frame 19 to rotate about the optical axis O relativeto the first lens group moving frame 18 due to the sliding movement ofeach follower pin 19 f of the second lens group moving frame 19 on thesurface XX of the inclined side edge β from the position “2 b” to theposition “3 b”. Namely, each linear guide key 19 a moves from theassociated circumferential recess 18 h toward the associated linearguide groove 18 c while sliding on the side surface (the lower surfaceas viewed in FIG. 10) of the associated circumferential recess 18 h.

Accordingly, if the second lens group moving frame 19 is rotatedrelative to the first lens group moving frame 18, the first lens groupmoving frame 18 can move forward smoothly without interfering with thesecond lens group moving frame 19.

Thereafter, each linear guide key 19 a comes into contact with a sideedge (the right side edge as viewed in FIG. 10) of the associated linearguide groove 18 c of the first lens group moving frame 18 to therebystop the rotation of the second lens group moving frame 19 (see theposition “3 c”). At this time, each linear guide key 19 a is ready toenter the associated linear guide groove 18 c of the first lens groupmoving frame 18, so that a further forward movement of the first lensgroup moving frame 18 causes the set of three linear guide key 19 a toenter the set of three linear guide grooves 18 c, respectively. Afterthe set of three linear guide keys 19 a have respectively entered theset of three linear guide grooves 18 c, the second lens group movingframe 19 is prevented from rotating about the optical axis O relative tothe first lens group moving frame 18 by engagement of each linear guidekey 19 a with the associated linear guide groove 18 c, while eachfollower pin 19 f of the second lens group moving frame 19 slides on thesurface XX of the inclined side edge β from the position “3 b” to “4 b”,which causes the second lens group moving frame 19 to move linearly in adirection opposite to the direction of movement of the first lens groupmoving frame 18 (see the position “4 b” in FIG. 10).

Further rotational movement of the cam ring 15 causes each follower pin19 f of the second lens group moving frame 19 to enter thefirst-lens-group accommodation section C1A1 of the associated lens-drivecam groove C1. Thereafter, if the cam ring 15 rotates in the directionX, the first and second lens group moving frames 18 and 19 move linearlyin the optical axis direction in accordance with the respective sectionsof the set of three lens-drive cam grooves C1 while the second lensgroup moving frame 19 is guided linearly in the optical axis directionby the first lens group moving frame 18. As can be understood from theabove description, the substantially triangular shaped second-lens-groupaccommodation section C1A2 of each lens-drive cam groove C1 not onlysecures a clearance for the associated follower pin 19 f to be movablefreely in both the circumferential direction of the cam ring 15 and theoptical axis direction within the triangular area, but also makes thesecond lens group moving frame 19 rotate relative to the first lensgroup moving frame 18 to lead each linear guide key 19 a to a positionso as to be engaged in the associated linear guide groove 18 c.Moreover, the substantially triangular shaped second-lens-groupaccommodation section C1A2 of each lens-drive cam groove C1 allows thefirst and second lens group moving frames 18 and 19 move in oppositedirections in the optical axis direction to ensure the proper engagementof the first lens group moving frame 18 with the second lens groupmoving frame 19.

On the other hand, in a state where the zoom lens barrel 1 is in aready-to-photograph state, if the cam ring 15 rotates in a direction toretract the zoom lens barrel 1, i.e., in a direction opposite to thedirection X, each follower pin 18 f and each follower pin 19 f return tothe first-lens-group accommodation section C1A1 and thesecond-lens-group accommodation section C1A2, respectively.

The movement of each follower pin will be hereinafter discussed indetail. After passing the first-lens-group accommodation section C1A1,each follower pin 19 f slides on the surface of a rear side edge α ofthe second-lens-group accommodation section C1A2 to move rightward withrespect to FIG. 10. Upon reaching a position on the surface of the rearside edge α immediately before an end al (the upper end as viewed inFIG. 9) thereof, each linear guide key 19 a comes out of the associatedlinear guide groove 18 c to enter the associated circumferential recess18 h, to thereby allow rotation of the second lens group moving frame 19relative to the first lens group moving frame 18 possible. Thereafter,each follower pin 19 f reaches the end α1 of the rear side edge α torotate about the optical axis O together with the cam ring 15, namely,the second lens group moving frame 19 rotates about the optical axis Orelative to the first lens group moving frame 18. Thereafter, since thecam ring 15 retreats in the optical axis direction (in the rightwarddirection with respect to FIG. 9) due to the engagement of the set ofthree follower pins 15 b with the linear slot portions 13 b 1 of the setof three cam slots 13 b of the stationary ring 13, each follower pin 19f finally reaches a terminal α2 in the vicinity of the end α1 of therear side edge α. In this manner, the first and second lens group movingframes 18 and 19 move to the respective accommodation positionssmoothly.

Assuming that the second lens group moving frame 19 is moved to theaccommodation position thereof with the second lens group moving frame19 being guided only linearly in the optical axis direction in a mannersimilar to that of the first lens group moving frame 18, each of thethree lens-drive cam grooves C1 has to be formed longer in acircumferential direction of the cam ring 15 (i.e., in an upwarddirection from the end α1 of the rear side edge α as viewed in FIG. 9).However, if the set of three lens-drive cam grooves C1 are simply formedlonger, theses grooves interfere with other cam grooves (e.g., the camgrooves C2). To prevent this problem from occurring, the diameter of thecam ring 15 has to be increased. However, according to the presentembodiment of the zoom lens barrel 1, the portion of each of the threelens-drive cam groove C1 which is used to accommodate the second lensgroup moving frame 19 can be designed short in a circumferentialdirection of the cam ring 15 within a range in which none of the threelens-drive cam grooves C1 interfere with other cam grooves. Thiscontributes to further miniaturization of the diameter of the cam ring15.

Since the second-lens-group accommodation section C1A2 of eachlens-drive cam groove C1 is formed having a substantially triangularshape, each lens-drive cam groove C1 is successfully formed as a shortcam groove, which would need to be longer if formed as a linear camgroove. In addition, by forming each lens-drive cam groove C1 as a shortgroove in such a manner, the set of three lens-drive cam grooves C1 canbe formed on the cam ring 15 with little inclination with respect to thecircumferential direction of the cam ring 15. Additionally, when thefirst and second lens group moving frames 18 and 19 move forward fromthe respective accommodation positions in the optical axis direction,each follower pin 19 f moves in the second-lens-group accommodationsection C1A2 from the position “1 b” to the position “4 b” via thepositions “2 b” and “3 b” in the above described manner while the secondlens group moving frame 19 rotates about the optical axis O relative tothe first lens group moving frame 18 because each lens-drive cam grooveC1 is provided with the substantially triangular shape second-lens-groupaccommodation section C1A2.

FIG. 15 shows the variation in the respective axial positions of firstand second lens group moving frames 18 and 19 in a range of movementincluding a zooming section (between telephoto extremity and wide-angleextremity) and a retracting section (between wide-angle extremity andaccommodation position). As can be understood from FIG. 15, the axialposition of the first lens group moving frame 18 corresponds to therotational position (angular position) of the cam ring 15 about theoptical axis O due to the profile of each lens-drive cam groove C1,while the second lens group moving frame 19 rotates about the opticalaxis O relative to the cam ring 15 in a range R shown in FIG. 15.

Friction produced between the light shield ring 19 c of the second lensgroup moving frame 19 and the first lens frame 20 becomes a problem ifthe second lens group moving frame 19 rotates relative to the first lensgroup moving frame 18 in the accommodation position because the firstlens frame 20, which is supported by the first lens group moving frame18, is in contact with the light shield ring 19 c at the mechanicallycontacting point P (see FIGS. 5 and 6). Such friction may cause thefirst lens frame 20 to rotate relative to the first lens group movingframe 18 to thereby deviate in the optical axis direction relative tothe first lens group moving frame 18 because the male thread portion ofthe first lens frame 20 is in mesh with the female thread portion 18 dof the inner flange 18 b. To prevent such deviation of the axialposition of the first lens frame 20 from occurring, the light shieldring 19 c is provided, on a front surface thereof with which a rear faceof the first lens frame 20 comes into contact, with a low-frictionalsheet (low-frictional portion) 26 (see FIGS. 5, 6 and 7) which can bemade of, e.g., a tetrafluoroethylene resin.

The overall movement of the zoom lens barrel 1, having the abovedescribed structure, from the accommodation position to aready-to-photograph position (a position in the zooming section) will behereinafter discussed. When the zoom lens barrel 1 is in anaccommodation state, the first lens frame 20 which is supported by thefirst lens group moving frame 18, which is biased rearward by the threehelical compression springs 30, is retracted to the mechanicallycontacting point P where the first lens frame 20 comes in contact withthe light shield ring 19 c of the second lens group moving frame 19 dueto the clearance between the first-lens-group accommodation section C1A1of each lens-drive cam groove C1 of the cam ring 15 and the associatedfollower pin 18 f of the first lens group moving frame 18. The secondlens group moving frame 19 is also retracted to the mechanicallycontacting point Q where the second lens group moving frame 19 comes incontact with the third lens frame 22 due to the clearance between thesecond-lens-group accommodation section C1A2 of each lens-drive camgroove C1 of the cam ring 15 and the associated follower pin 19 f of thesecond lens group moving frame 19. Furthermore, the third lens frame 22is retracted to the mechanically contacting point R wherein the thirdlens frame 22 comes in contact with the housing 11 by the spring forceof the helical compression spring 23 which presses the third lens frame22 forward. With these three mechanical contacts at the mechanicallycontacting points P, Q and R, the length of the zoom lens barrel 1 in anaccommodation state of the zoom lens barrel 1 is successfully reduced.When the zoom lens barrel 1 is in an accommodation state, the pair ofbarrier blades 42 are closed to shut the photographing aperture 41 a(see FIG. 12), since the three rotation transfer faces 15 d respectivelypress the three engaging portions 31 a of the barrier drive ring 31against the spring force of the helical extension spring 45 to rotatethe barrier drive ring 31 in a direction to move the two driveprojections 31 c away from the two engaging projections 42 a of the pairof barrier blades 42, respectively.

In the accommodation state of the zoom lens barrel 1, if the rotatablering 14 rotates in a direction to extend the zoom lens barrel 1 relativeto the stationary ring 13, the cam ring 15 which is provided with theset of three follower pins 15 b, moves in the optical axis directionwithout rotating about the optical axis O due to the engagement of thefollower pins 15 b of the cam ring 15 with the inclined groove portions14 a 2 of the rotatable ring 14 and the linear slot portions 13 b 1 ofthe stationary ring 13 (see FIG. 11). This linear movement of the camring 15 causes a side edge of the first-lens-group accommodation sectionC1A1 of each lens-drive cam groove C1 to push the associated followerpin 18 f forward, and at the same time, causes a side edge of thesecond-lens-group accommodation section C1A2 of each lens-drive camgroove C1 to push the associated follower pin 19 f forward. As a result,the first lens frame 20 and the second lens group moving frame 19 (thelight shield ring 19 c) which are in contact with each other at themechanically contacting point P move linearly forward to release thecontact therebetween, while the second lens group moving frame 19 whichis in contact with the third lens frame 22 at the mechanicallycontacting point Q moves forward linearly to release the contact betweenthe second lens group moving frame 19 with the third lens group L3.

If the rotatable ring 14 further rotates in the same direction to extendthe zoom lens barrel 1 relative to the stationary ring 13, the cam ring15 moves in the optical axis direction while rotating about the opticalaxis O due to the engagement of the follower pins 15 of the cam ring 15with the linear groove portions 14 a 1 of the rotatable ring 14 and thestate-changing slot portions 13 b 2 of the stationary ring 13, until therotatable ring 14 reaches the zooming section. In an early state of thisrotation of the cam ring 15 by the state-changing slot portions 13 b 2of the stationary ring 13, the three rotation transfer faces 15 d of thecam ring 15 are respectively disengaged from the three engaging portions31 a of the barrier drive ring 31 so that the barrier drive ring 31 isrotated in a direction to open the pair of barrier blades 42 by thespring force of the helical extension spring 45 against the spring forceof the two torsion springs 43. Accordingly, the second lens group movingframe 19 rotates about the optical axis O relative to the first lensgroup moving frame 18 so that the first lens frame 20 slides on thelow-frictional sheet 26 before and after the opening operation of thepair of barrier blades 42.

When each follower pin 15 b of the cam ring 15 reaches the zooming slotportion 13 b 3 of the associated cam slot 13 b by rotation of therotatable ring 14 in the same rotational direction, rear faces(contacting surfaces) 32 b of the set of three inward projections 32 cof the biasing ring 32 come into contact with the set of three followerpins 15 b of the cam ring 15, respectively (see the zoom lens barrel 1below the optical axis O in FIG. 7). Each follower pin 15 b is pressedagainst the rear side edge of the zooming slot portion 13 b 3 of theassociated cam slot 13 b by the rear face 32 b of the associated inwardprojection 32 c since the biasing ring 32 is biased rearward by thethree helical extension springs 33. This state is maintained as long aseach follower pin 15 b is engaged in the zooming slot portion 13 b 3 ofthe associated cam slot 13 b, while backlash and play of the cam ring 15with respect to the stationary barrel 13 is removed as long as the camring 15 rotates within the zooming section shown in FIG. 11 via therotatable ring 14.

If the cam ring 15 rotates in a direction from the accommodationrotational position to the zooming section via the preparation section(i.e., in the barrier opening direction), each follower pin 18 f of thefirst lens group moving frame 18 which is engaged in thefirst-lens-group accommodation section C1A1 moves from thefirst-lens-group accommodation section C1A1 to the first-lens-groupzooming section C1Z1 via the second-lens-group zooming section C1Z2,while each follower pin 19 f of the second lens group moving frame 19which is engaged in the second-lens-group accommodation section C1A2moves from the second-lens-group accommodation section C1A2 to thesecond-lens-group zooming section C1Z2 via the first-lens-groupaccommodation section C1A1. If the cam ring 15 rotates in the zoomingrange (i.e., in the first-lens-group zooming section C1Z1 and thesecond-lens-group zooming section C1Z2), the first and second lens groupmoving frames 18 and 19 (the first and second lens groups L1 and L2)move in the optical axis direction in respective zoom paths thereof inaccordance with the profiles of the first-lens-group zooming sectionC1Z1 and the second-lens-group zooming section C1Z2, to thereby vary thefocal length of the photographing optical system which includes thefirst, second and third lens groups L1, L2 and L3, i.e., to perform azooming operation. This zooming operation is carried out by manuallyoperating a conventional zoom switch (not shown). Immediately after arelease button is depressed, the aforementioned step motor (not shown),which drives feed screw 24 to move the third lens frame 22 (the thirdlens group L3), rotates by an amount of rotation corresponding toinformation on a photographing distance to move the third lens group Lto bring an object into focus. The shutter unit 21 drives the shutterblades 21 a to open and close in accordance with the information on theobject brightness.

If the first lens group moving frame 18 moves linearly in the opticalaxis direction, the inner ring 17 also moves in the optical axisdirection without varying the position thereof relative to the firstlens group moving frame 18 due to the engagement of the set of threefollower pins 17 f with the set of three cam grooves C2 of the cam ring15, the profiles of which are similar to those of the lens-drive camgrooves C1. At the same time, the outer ring 16 and the inner ring 17,the respective outer peripheral surfaces of which are exposed to theoutside of the zoom lens barrel 1, move together in the optical axisdirection since the outer ring 16 moves together with the cam ring 15 inthe optical axis direction at all times due to the engagement of the setof three bayonet prongs 16 d with the circumferential groove 15 c.

If the cam ring 15 rotates in a direction from the zooming section viathe preparation section (i.e., in the barrier closing direction), theouter and inner rings 16 and 17 retract together in the optical axisdirection by operations reverse to the above described operations.Subsequently, the first lens frame 20, which supports the first lensgroup L1, and the second lens group moving frame 19, which supports thesecond lens group L2, come into contact with each other at theirrespective rear ends via the three helical compression springs 30, whilethe second lens group moving frame 19 retreats until coming into contactwith the third lens frame 22 to push the third lens frame 22 against thefilter holding portion 11 c against the helical compression spring 23,which presses the third lens frame 22 forward. At the same time, thethree rotation transfer faces 15 d respectively press the three engagingportions 31 a of the barrier drive ring 31 against the spring force ofthe helical extension spring 45 to rotate the barrier drive ring 31 in adirection to close the pair of barrier blades 42 to shut thephotographing aperture 41 a.

As has been described above, in the present embodiment of the zoom lensbarrel, assuming that the second lens group moving frame 19 is moved tothe accommodation position thereof with the second lens group movingframe 19 being guided only linearly in the optical axis direction in amanner similar to that of the first lens group moving frame 18, each ofthe three lens-drive cam grooves C1 has to be formed longer in acircumferential direction of the cam ring 15. However, if the set ofthree lens-drive cam grooves C1 are simply formed longer, these grooveswould interfere with other cam grooves (e.g., the cam grooves C2). Toprevent this problem from occurring, the diameter of the cam ring 15 hasto be increased. However, according to the present embodiment of thezoom lens barrel 1, the portion of each of the three lens-drive camgroove C1 which is used to accommodate the second lens group movingframe 19 can be designed short in a circumferential direction of the camring 15 within a range in which none of the three lens-drive cam groovesC1 interfere with other cam grooves. This contributes to furtherminiaturization of the diameter of the cam ring 15.

In the present embodiment of the zoom lens barrel, although the flexiblePWB 21 b is twisted when the second lens group moving frame 19 rotates,the flexible PWB 21 b is not damaged because the flexible PWB 21 b isfixed to the shutter unit 21 that rotates together with the second lensgroup moving frame 19. Therefore, a driving signal information on anobject brightness can be reliably transmitted to the shutter unit 21 viathe flexible PWB 21 b to open and close the shutter blades 21 a.

In addition, the above described structure wherein the bending portion21 bx of the flexible PWB 21 b passes through the rubber band 29, whichpulls the bending portion 21 bx obliquely rearwards in a direction awayfrom the optical axis O, prevents the flexible PWB 21 b from bending andinterfering with the photographing optical path of the zoom lens barrel1.

In the present embodiment of the zoom lens barrel, when the first andsecond lens group moving frames 18 and 19 retreat to the accommodatedpositions thereof as shown in FIG. 6, the three linear guide keys 19 aare loosely fitted in the three circumferential slots 18 j, and thefirst lens group moving frame 18 retreats until the three linear guidekeys 19 a respectively project forward from the front ends of the threecircumferential slots 18 j. This structure makes it possible for thefirst and second lens moving frames 18 and 19 to be accommodated ascompact as possible.

As has been described above, friction produced between the light shieldring 19 c of the second lens group moving frame 19 and the first lensframe 20 becomes a problem when the second lens group moving frame 19rotates relative to the first lens group moving frame 18 in theaccommodation position because the first lens frame 20 is in contactwith the light shield ring 19 c at the mechanically contacting point P.Such friction may cause the first lens frame 20 to rotate relative tothe first lens group moving frame 18 to thereby deviate in the opticalaxis direction relative to the first lens group moving frame 18 becausethe male thread portion of the first lens frame 20 is in mesh with thefemale thread portion 18 d of the inner flange 18 b. In the presentembodiment of the zoom lens barrel, to prevent such deviation of theaxial position of the first lens frame 20 from occurring, thelow-frictional sheet 26 that is made of e.g., a tetrafluoroethyleneresin is fixed to the front surface of the light shield ring 19 c, towhich the rear face of the first lens frame 20 comes into contact. Inthe accommodation state of the zoom lens barrel 1 shown in FIGS. 5 and6, the low-frictional sheet 26 is held between the first lens frame 20and the light shield ring 19 c. The low-frictional sheet 26 can be madeof any other material than a tetrafluoroethylene resin. Thelow-frictional sheet 26 can be a sheet wherein the contacting surface ofwhich is coated with a low-frictional resin such as a low-frictionalfluoroplastic. The low-frictional sheet 26 can be fixed to a rearsurface of the first lens frame 20 instead of the light shield ring 19c.

In the present embodiment of the zoom lens barrel, upon being rotated,the cam ring 15 positioned at the accommodation position thereof firstlymoves linearly in the optical axis direction without rotating about theoptical axis O to release biasing forces applied to the first and secondlens group moving frames 18 and 19 at the respective accommodationpositions thereof, subsequently moves in the optical axis directionwhile rotating about the optical axis O, and finally the cam ring 15rotates about the optical axis O without moving in the optical axisdirection. Due to this structure, the cam ring 15 does not interferewith any peripheral elements in a predetermined moving section of thecam ring 15 from the fully-retracted position thereof even if the zoomlens barrel 1 is constructed as compact as possible.

In the present embodiment of the zoom lens barrel, when the cam ring 15retreats linearly in the optical axis direction toward the accommodationposition thereof, the inner ring 17 moves together with the cam ring 15to thereby increase the biasing force of the helical compression springs30. This causes the first lens frame 20, which is fixed to the firstlens group moving frame 18, and the second lens group moving frame 19 tomake sure contact with each other, and at the same time, causes thesecond lens group moving frame 19 and the third lens frame 22 to makesure contact with each other.

In the present embodiment of the zoom lens barrel, with a simplestructure, backlash is reliably prevented from occurring between the camring 15 and the guiding mechanism for guiding the cam ring 15 in theoptical axis direction, in a predetermined moving section thereof suchas the zooming section shown in FIG. 11 where a high optical performanceis required. This simple structure improves the performance of thefocusing system of the zoom lens barrel 1.

In addition, the cam ring 15 is not biased to remove such backlash atall times; the set of three follower pins 15 b of the cam ring 15 arefree from the biasing force applied thereto via the set of three inwardprojections 32 c, and are loosely engaged in either the linear slotportions 13 b 1 or the state-changing slot portion 13 b 2 of the set ofcam slots 13 b, so that the cam ring 15 rotates about the optical axisand moves in the optical axis direction smoothly when the zoom lensbarrel 1 retracts to an accommodation position and advances to aready-to-photograph position.

Although the set of linear guide grooves 18 c and the set ofcircumferential recesses 18 h are formed on the first lens group movingframe 18 while the set of linear guide keys 19 a are formed on thesecond lens group moving frame 19, a set of linear guide grooves and aset of circumferential recesses which are respectively correspond to theset of linear guide grooves 18 c and the set of circumferential recesses18 h can be formed on the second lens group moving frame 19 while a setof linear guide keys corresponding to the set of linear guide keys 19 acan be formed on the first lens group moving frame 18.

The rubber band 29 can be substituted by any other elastic band.

The present invention can be applied not only to a zoom lens barrel butalso to a fixed-focal-length lens barrel having a ring member whichprojects from and retracts into a camera body.

The above described linear guiding mechanism for guiding the first andsecond lens group moving frames 18 and 19 and the inner ring 17 in theoptical axis direction without rotating about the optical axis O is notlimited solely to such a particular mechanism as long as the generalconcept of the two sets of lens-drive cam grooves C1 and C2 is appliedto the lens barrel. Although the set of three lens-drive cam grooves C1are formed on the cam ring 15 in the above illustrated embodiment of thezoom lens barrel 1, a similar effect can be expected with only onelens-drive cam groove C1 in theory. Likewise, although the set of threelens-drive cam grooves C2 are formed on the cam ring 15 in the aboveillustrated embodiment of the zoom lens barrel 1, a similar effect canbe expected with only one lens-drive cam groove C2 in theory.

As can be understood from the foregoing, according to the presentinvention, a lens barrel is achieved which has front and rear lensgroups and also a cam ring on which cam grooves for driving the frontand rear lens groups are formed, wherein front and rear lens groups canbe driven to move forward smoothly from their respective accommodationpositions in an optical axis direction by rotation of the cam ring evenif the angle of inclination of each cam groove formed thereon withrespect to a circumferential direction of the cam ring is small.

Moreover, in a type of lens barrel in which the respective lens groupmoving frames of front and rear lens groups are driven to rotaterelative to each other while remaining in contact with each other toretract the front and rear lens groups to their respective accommodationpositions, the friction produced between the contacting surfaces of thetwo lens group moving frames can be made minimal.

Furthermore, since the cam ring is prohibited from rotating in apredetermined moving section of the cam ring from a fully retractedposition thereof, the cam ring is prevented from interfering with anyperipheral elements while moving in the optical axis direction in thepredetermined moving section.

Furthermore, backlash is prevented from occurring between the cam ringand a guiding mechanism for guiding the cam ring in the optical axisdirection.

Obvious changes may be made in the specific embodiment of the presentinvention described herein, such modifications being within the spiritand scope of the invention claimed. It is indicated that all mattercontained herein is illustrative and does not limit the scope of thepresent invention.

What is claimed is:
 1. A lens barrel comprising: a front lens framewhich supports a front lens group and includes a first cam follower,said front lens frame being guided linearly in an optical axis directionwithout rotating about said optical axis; a rear lens frame whichsupports a rear lens group and includes a second cam follower; a camring driven to rotate about said optical axis, said cam ring including afirst cam groove and a second cam groove in which said first camfollower and said second cam follower are respectively engaged; saidfirst cam groove including a first moving section for moving said frontlens frame in said optical axis direction, and a first accommodationsection for moving said front lens frame behind a position of said frontlens frame of which said first follower is engaged in said first movingsection; said second cam groove including a second moving section formoving said rear lens frame in said optical axis direction, and a secondaccommodation section for moving said rear lens frame behind a positionof said rear lens frame of which said second follower is engaged in saidsecond moving section, said second accommodation section including anaccommodation position at which said rear lens frame is positionedrearmost; and a multi-direction guiding mechanism, provided between saidfront lens frame and said rear lens frame, for allowing said rear lensframe to rotate about said optical axis relative to said front lensframe when said second cam follower is engaged in a vicinity of saidaccommodation position of said second accommodation section, and forprohibiting said rear lens frame from rotating about said optical axisrelative to said front lens frame while allowing said rear lens frame tomove only in said optical axis direction relative to said front lensframe when said second cam follower is engaged in a section of saidsecond cam groove which includes said second moving section and excludessaid vicinity of said accommodation position.
 2. The lens barrelaccording to claim 1, further comprising: a shutter unit fixed to saidrear lens frame; and a flexible PWB which extends rearward from saidshutter unit so that a drive signal can be transmitted to said shutterunit via said flexible PWB.
 3. The lens barrel according to claim 2,further comprising an elastic band which is engaged with said flexiblePWB to pull a portion of said flexible PWB in a direction away from saidoptical axis.
 4. The lens barrel according to claim 3, wherein saidelastic band comprises a rubber band.
 5. The lens barrel according toclaim 1, wherein said multi-direction guiding mechanism comprises: alinear guide groove formed on an inner peripheral surface of said frontlens frame to extend parallel to said optical axis; arotation-permitting groove, formed at a front end of said linear guidegroove, which communicatively connects with said linear guide groove, awidth of said rotation-permitting groove being greater than a width ofsaid linear guide groove in a circumferential direction of said frontlens frame; and a linear guide projection, formed on said rear lensframe, which is engaged in said rotation-permitting groove when saidsecond cam follower is engaged in said vicinity of said accommodationposition, and which is engaged in said linear guide groove when saidsecond cam follower is engaged in said section of said second cam groovewhich includes said second moving section and excludes said vicinity ofsaid accommodation position.
 6. The lens barrel according to claim 5,wherein said front lens frame comprises an inner flange for supportingsaid front lens group, a circumferential opening being formed on saidfront lens frame; and wherein said rear lens frame comprises a frontprojecting portion, on which said linear guide projection is formed,said front projecting portion projecting forward to extend through saidinner flange through said circumferential opening when said second camfollower is engaged in said vicinity of said accommodation position. 7.The lens barrel according to claim 6, wherein said inner flange isformed on said front lens frame at a front end thereof.
 8. The lensbarrel according to claim 1, wherein said lens barrel comprises a zoomlens barrel; wherein said first moving section and said second movingsection constitute a first zooming section and a second zooming sectionfor moving said front lens group and said rear lens group to perform azooming operation, respectively.
 9. The lens barrel according to claim1, wherein said rear lens frame rotates about said optical axis viarotation of said cam ring when said second cam follower is engaged insaid vicinity of said accommodation position.
 10. A lens barrelcomprising: a front lens frame which supports a front lens group andincludes a first cam follower, said front lens frame being guidedlinearly in an optical axis direction without rotating about saidoptical axis; a rear lens frame which supports a rear lens group andincludes a second cam follower; a cam ring driven to rotate about saidoptical axis, said cam ring including a continuous cam groove in whichsaid first cam follower and said second cam follower are engaged;wherein said continuous cam groove includes a first moving section formoving said front lens group in said optical axis direction; a firstaccommodation section for moving said front lens frame behind a positionof said front lens frame of which said first follower is engaged in saidfirst moving section; a second moving section for moving said rear lensgroup in said optical axis direction; and a second accommodation sectionfor moving said rear lens frame behind a position of said rear lensframe of which said second follower is engaged in said second movingsection, said second accommodation position including an accommodationposition at which said rear lens frame is positioned rearmost, in thatorder from one end of said continuous cam groove; and a guidingmechanism for allowing said rear lens frame to rotate about said opticalaxis relative to said front lens frame when said second cam follower isengaged in a vicinity of said accommodation position of said secondaccommodation section, and for prohibiting said rear lens frame fromrotating about said optical axis relative to said front lens frame whileallowing said rear lens frame to move only in said optical axisdirection relative to said front lens frame when said second camfollower is engaged in a section of said second cam groove whichincludes said second moving section and excludes said vicinity of saidaccommodation position; wherein said second accommodation section isformed to firstly make said rear lens frame move in said optical axisdirection while making said rear lens frame rotate about said opticalaxis relative to said front lens frame via said second cam followerengaged in said second accommodation section, and to subsequently makesaid front lens frame guide said rear lens frame in said optical axisdirection without making said rear lens frame rotate about said opticalaxis when said first cam follower of said front lens frame moves fromsaid first accommodation section to said second moving section byrotation of said cam ring.
 11. The lens barrel according to claim 10,wherein said lens barrel comprises a zoom lens barrel; wherein saidfirst moving section and said second moving section constitute a firstzooming section and a second zooming section for moving said front lensgroup and said rear lens group to perform a zooming operation,respectively.
 12. The lens barrel according to claim 10, wherein saidguiding mechanism comprises: a guiding portion formed on said front lensframe, wherein said front lens frame firstly comes into contact withsaid rear lens frame and subsequently presses said rear lens frame tomove said rear lens frame forward in said optical axis direction whensaid first cam follower passes said second moving section while movingfrom said first accommodation section toward said first moving section;and an engaging portion formed on said rear lens frame, said engagingportion being engaged with said guiding portion to be guided linearly insaid optical axis direction by said guiding portion, wherein a side edgeof said second accommodation section firstly comes into contact withsaid second cam follower, and subsequently said side edge presses saidsecond cam follower to rotate said rear lens frame about said opticalaxis so that said engaging portion enters said guiding portion when saidrear lens frame is moved forward by said front lens frame.